Astro&109&Lecture&2:& An&Insider’s&View&of&Science&ajbaker/ph109/midterm/Lec02-Sep05-F14+key.pdfOrganizaonal&reminders& • Oﬃce&hours&are&Friday&3:00a4:30pm&in&ScoW&Hall&...

Astro 109 Lecture 2: An Insider’s View of Science

September 5, 2014

ConstellaBon of the day: Cepheus •  This is a “circumpolar” constellaBon: it is close to the north celesBal pole, and therefore visible at night all year.

•  Named aLer a mythological African king who nearly sacrificed his daughter (Andromeda) to a sea monster. Image credit: IAU/Sky & Telescope

Why astronomers like Cepheus

•  Its fourth brightest star (δ Cephei) is the prototypical Cepheid variable: every 5.4 days, it goes through a pulsaBon cycle in which its brightness varies by a factor of 2.3.

•  HenrieWa Swan LeaviW (1868–1921) showed that the period of a Cepheid variable can be used to predict its luminosity – a relaBonship that astronomers sBll exploit today to measure the distances to other galaxies!

Image credit: Wikimedia Commons Image credit: AAVSO

OrganizaBonal reminders

•  Office hours are Friday 3:00-‐4:30pm in ScoW Hall 102, and Tuesday 4:00-‐5:30pm in Serin Physics and Astronomy Building 401.

•  Reading for next Wednesday: SecBon 2.1. •  Please buy a clicker and register it in Sakai!

Sign up for next week’s study groups! •  QuesBons to prepare to discuss with LAs:

–  How far away are planets, stars, and galaxies? –  What makes an acBvity “science,” and what makes someone a scienBst?

•  QuesBons from last year’s midterm you should be able

to answer aLer today’s lecture: #12 (c = λν), #18, #28

•  Homework # 1 will be available in Sakai right aLer today’s class, and is due before next Friday’s class.

•  SuggesBon from LAs: bring your textbook and a paper copy of last year’s midterm.

Scheduling of weekly study groups LA DAY TIME CAMPUS ROOM

Elsie Lee Monday 1:10-‐2:30pm College Ave Kreeger 117

Isabel Kennedy Monday 6:40-‐8:00pm Livingston TilleW 111

Ryan DeGregorio Tuesday 8:10-‐9:30pm Busch ARC 326

Adrian Casper Wednesday 1:10-‐2:30pm College Ave Kreeger 117

Zac Csorny Wednesday 2:50-‐4:10pm College Ave Kreeger 117

Ragen Patel Thursday 2:50-‐4:10pm College Ave Kreeger 117

Anthony Xing TBD TBD TBD TBD

•  If none of these Bmes work for you, please email me. The seventh study group or my office hours may work instead.

Clicker quesBons

•  Let you engage in acBve learning, just like scienBsts.

•  Help you keep up with the course material and think more deeply about certain topics.

•  When I pose a quesBon… –  You’ll vote using your i>clicker. – We’ll look at the distribuBon of answers. – We’ll discuss the results, and maybe revote. –  You’ll earn points (3 = correct answer, 2 = correct answer aLer a revote, 1 = incorrect answer).

How does the voBng process work? •  First: turn on your i>clicker!

•  I will read a quesBon and the five possible responses, and then start the Bmer (typically, 45 seconds).

•  You can change your answer as many Bmes as you want while the Bmer is running.

•  If we have a revote, I will ask you to discuss the quesBon with your neighbor(s). Don’t sit by yourself!

A few i>clicker Bps

•  Write your iniBals or name on your i>clicker.

•  If you bought a used i>clicker, replace the baWeries.

•  If you bought a new i>clicker and it doesn’t want to turn on, check that the baWeries have good contact with the rest of the device.

•  Check out hWp://www1.iclicker.com/ for more info.

Sample quesBon

What is your class year?

A.  freshman B.  sophomore C.  junior D.  senior E.  other

Sample quesBon

What area is your major?

A.  arts or humaniBes B.  social science C.  science or engineering D.  other E.  undecided

Sample quesBon

How you feel about math?

A.  I try to avoid it as much as possible. B.  I deal with it if I have to. C.  I like it OK, but it’s not my favorite subject. D.  (-‐1)0.5 like it a lot! E.  π

Sample quesBon

Did you take any sort of physics course in high school?

A.  I’ve never taken any kind of physics course. B.  I took physical science in high school. C.  I took one year of physics in high school. D.  I took two or more years of physics in high school. E.  Does physical educaBon (PE) count?

ScienBfic Reasoning

Science and scienBsts

•  ScienBsts are people, who are trying to generate knowledge. –  I was like a boy playing on the sea-‐shore, and diver9ng myself now and then

finding a smoother pebble or a pre<er shell than ordinary…. – Isaac Newton –  We are driven by the usual insa9able curiosity of the scien9st, and our work is

a delighAul game. – Murray Gell-‐Mann

•  Science is an insBtuBon, which provides a framework for evaluaBng knowledge. –  There are many hypotheses in science which are wrong. That’s perfectly all

right; they’re the aperture to finding out what’s right. Science is a self-‐correc9ng process. To be accepted, new ideas must survive the most rigorous standards of evidence and scru9ny. – Carl Sagan

Science as a way of knowing

•  Science: (Webster’s New World Dic9onary, 2ed)

–  “systemaBzed knowledge derived from observaBon, study, and experimentaBon carried out in order to determine the nature or principles of what is being studied”

•  Focus on specific ideas that can be tested with reproducible experiments/observaBons.

Science is a way of thinking much more than it is a body of knowledge. – Carl Sagan

Hallmarks of science

•  ExplanaBons –  “Modern science seeks explana9ons for observed phenomena that rely

solely on natural causes.”

•  Models and simplicity –  “Science progresses through the crea9on and tes9ng of models of

nature that explain the observa9ons as simply as possible.”

•  Testable predicBons –  “A scien9fic model must make testable predic9ons about natural

phenomena that will force us to revise or abandon the model if the predic9ons do not agree with the observa9ons.”

Cornerstones of explanaBon

•  Causality –  Everything that happens has a natural cause.

•  Universality –  The laws we have discovered on Earth hold everywhere and everywhen. –  Astronomy puts this to the test!

The most incomprehensible thing about the world is that it is comprehensible. – Albert Einstein

ExplanaBons / Models and simplicity / Testable predicBons

ScienBfic models

•  Simplified representaBons of reality.

•  Not “true” in an absolute sense, but can be useful.

•  Examples for planetary moBons: –  geocentric model: planets and Sun move around Earth –  heliocentric model: planets move around Sun –  gravitaBonal model (based on Newton’s theory of gravity): Sun and planets move in response to each other


Clicker quesBon # 1

A scienBfic model…

A.  can be constructed using Legos. B.  can only be described in terms of equaBons. C.  doesn’t have to be 100% correct to be useful. D.  doesn’t have any connecBon to reality. E.  is filmed for ads that run on Discovery Channel.

Simplicity: Occam’s Razor

•  Roughly: “The simplest explanaBon is probably the correct one.”

•  BeWer: “When faced with compeBng hypotheses that are otherwise equal, pick the one with the fewest new assumpBons.”

•  A rule of thumb, especially for developing new models. Not a rigorous principle of logic.


Clicker quesBon # 2

Occam’s Razor is…

A.  a Bebreaker in deciding which of two different sets of data to trust.

B.  a Bebreaker in deciding which of two different models to favor.

C.  the principle that a good scienBfic model should be simple. D.  the principle that a good scienBfic model should fit the

data. E.  best used with lots of shaving cream.

Testable predicBons

•  A good model should explain what is already known … and predict something specific that is not yet known.

•  This is key to evaluaBng ideas in science.

•  This is also where pseudoscience usually fails!

•  Not everything is predictable in fine detail. –  weather, climate, stock market, personal rela9onships, … –  just too many factors


It doesn’t maTer how beau9ful your theory is. It doesn’t maTer how smart you are. If it doesn’t agree with experiment, it’s wrong. – Richard Feynman

ScienBfic Method (idealized)

Sept. 4

“hypothesis” = educated guess

•  My flashlight no longer works.

•  Are the baWeries to blame?

•  The flashlight needs new baWeries.

•  With new baWeries the flashlight will work.

•  Add new baWeries. Does it work? Yes – done. No – new idea…

Sept. 4

Hypothesis, Theory, Paradigm •  Hypothesis = educated guess

•  Theory = powerful model that uses simple principles to explain many observaBons, which has survived repeated and varied tesBng –  Newton’s theory of gravity –  Einstein’s theory of rela9vity –  Darwin’s theory of evolu9on

•  Paradigm = general paWern of thought –  Newtonian physics –  Rela9vis9c physics –  Quantum physics


Reproducibility and falsifiability

•  Experiments and observaBons should be reproducible. –  If they aren’t, their data aren’t useful for tesBng models.

•  ScienBfic theories cannot be proved – only disproved – so models should be falsifiable. –  If they aren’t, they can’t be usefully tested by data.

•  Untenable ideas must be discarded. –  No person is too “great” to be challenged. –  No idea is sacrosanct if it conflicts with solid experimental evidence.

No amount of experimenta9on can ever prove me right; a single experiment can prove me wrong. – Albert Einstein


An example of falsificaBon

•  DisBnguished theoreBcal physicist Dr. X develops a creaBve, elegant, and sophisBcated model that explains many aspects of parBcle physics. If correct, the model might merit a Nobel Prize!

•  A team of experimental physicists makes a single new measurement that disagrees with a predicBon of Dr. X’s model.

•  Dr. X’s model is dead. His reacBon: “He who cannot cast away a treasure in need is in feWers.”


Clicker quesBon # 3 Your professor proposes the hypothesis that all the geese at Rutgers live on Busch Campus. What is the most compelling scienBfic evidence against this hypothesis? A.  You take a cell phone picture of a goose on Livingston

Campus. B.  A Nobel-‐prize-‐winning biologist from Harvard writes in the

New York Times that the hypothesis is rubbish. C.  Your roommate remembers seeing a goose on Cook Campus

last weekend. D.  The staBsBcal analysis of a Rutgers business school professor

suggests that the hypothesis is probably incorrect. E.  Your professor also claims to have been abducted by aliens.

ScienBfic Method (idealized)

Sept. 4

How I feel about the “scienBfic method”

Image credit: Wikipedia

Reality check # 1: friendly compeBBon Image credit: The BuTer BaTle Book, Dr. Seuss

Some scienBsts (experimenters and observers) try to obtain new data that can falsify models.

Some scienBsts (theorists) try to improve models, so that they can successfully match all data.

Reality check # 2: pure curiosity works, too

“I don’t know exactly where I’m going, but this sure smells interesBng! I wonder what will happen if I wander off in this direcBon…”

Image credit: hWp://www.yourpurebredpuppy.com/

Reality check # 3: someBmes data are bad

•  The astronomer Percival Lowell (discoverer of Pluto) recorded observaBons of “spokes” on the clouds of Venus.

•  Modern astronomers see no spokes on Venus. (In fact, readers of a 2003 Sky and Telescope arBcle deduced that Lowell was seeing the projecBon of structures inside his own eyeball!) Image credit:

Lowell Observatory

Reality check # 4: not all data are available

•  As examples, we can’t… –  observe the Milky Way from above (at least, not yet) –  reproduce the exact condiBons of the Big Bang –  repeat the formaBon of the solar system to test models

•  …although we try to get around such limits by… –  observing many other galaxies that we assume look like the Milky Way

–  combining many observaBons of the distant universe to make inferences about the Big Bang

–  studying many planetary systems in formaBon around other stars, which we assume look like ours used to

Reality check # 5: usually, it’s not just you!

CollaboraBon and teamwork is a hallmark of modern science (e.g., huge teams at the Large Hadron Collider).

Image credit: CMS collaboraBon

QuanBtaBve Analysis

Power-‐of-‐10 notaBon

•  A convenient way to express very large and very small numbers, and to compute with them.

giga 109 1 000 000 000 mega 106 1 000 000 kilo 103 1 000 – 100 1

cenB 10-‐2 0.01 milli 10-‐3 0.001 micro 10-‐6 0.000 001 nano 10-‐9 0.000 000 001

CompuBng with powers of 10

3000000⇥ 500 = (3⇥ 106)⇥ (5⇥ 102)

= (3⇥ 5)⇥ (106 ⇥ 102)

= 15⇥ 106+2

= 1.5⇥ 10⇥ 108

= 1.5⇥ 109

What do you get when you mulBply 2×1022 by 3×10-‐10?

A.  a headache

B.  6×1012

C.  6×1032

D.  5×1012

E.  5×1032

Clicker quesBon # 4

Units

•  Units are as important as numbers! Always keep track of units!

•  SI units (metric system) –  length: meter or kilometer –  mass: gram or kilogram –  Bme: second or year –  angle: degree, arcmin, or arcsec

•  Convert units by mulBplying by 1.

Example

•  How many seconds are there in a day?

1 d⇥ 24 hr

1 d⇥ 60 min

1 hr⇥ 60 sec

1 min= 86400 sec

Note how we can convert units. Always keep track of units!

Astronomers’ units

Length

•  Astronomical Unit (AU) = average distance between Earth and Sun

•  light-‐year (ly) = distance light travels in 1 year

•  parsec (pc) = 3.26 light-‐years

1 AU = 1.496⇥ 108 km

1 ly =�3⇥ 105 km s�1�⇥

✓1 yr⇥ 365 d

1 yr⇥ 86400 s

1 d

◆= 9.46⇥ 1012 km

Millenium Falcon pilot Han Solo has boasted that his ship is so fast it “made the Kessel Run in less than 12 parsecs.” Why might an astronomer find this statement suspicious?

A.  A parsec is a completely made-‐up unit. B.  A parsec is a unit always counted in mulBples of ten. C.  A parsec is a unit of mass, not a unit of Bme. D.  A parsec is a unit of distance, not a unit of Bme. E.  Han Solo is not a Jedi.

Clicker quesBon # 5

Astronomers’ units

Mass

•  Sun

•  Jupiter •  Earth

M� = 1.99⇥ 1030 kg

MJ = 1.90⇥ 1027 kg

M� = 5.97⇥ 1024 kg

Scheduling: weekly study groups LA DAY TIME CAMPUS ROOM

Elsie Lee Monday 1:10-‐2:30pm College Ave Kreeger 117

Isabel Kennedy Monday 6:40-‐8:00pm Livingston TilleW 111

Ryan DeGregorio Tuesday 8:10-‐9:30pm Busch ARC 326

Adrian Casper Wednesday 1:10-‐2:30pm College Ave Kreeger 117

Zac Csorny Wednesday 2:50-‐4:10pm College Ave Kreeger 117

Ragen Patel Thursday 2:50-‐4:10pm College Ave Kreeger 117

Anthony Xing TBD TBD TBD TBD

•  If none of these Bmes work for you, please email me. The seventh study group or my office hours may work instead.

Astro&109&Lecture&2:& An&Insider’s&View&of&Science&ajbaker/ph109/midterm/Lec02-Sep05-F14+key.pdfOrganizaonal&reminders& • Oﬃce&hours&are&Friday&3:00a4:30pm&in&ScoW&Hall&...

Documents